Method and apparatus for altering frequency components of a transformed signal, and a recording medium therefor

ABSTRACT

A signal transforming method and apparatus which improves the quality of a signal, and a recording medium therefore. This method and apparatus alters the frequency components of an acoustic time signal. By altering the frequency components the characteristics of the acoustic time signal is transformed such that its quality is improved. The alteration is such that the difference in magnitude of attributes of frequency components within a substantially critical band are adjusted based on characteristics of auditory sensing.

TECHNICAL FIELD

This invention relates to a signal transforming method and a signaltransforming apparatus applied to, e.g., digital audio equipments andadapted for altering (changing) sound quality (i.e., transforming thecharacteristic of time signal information) by using particularly theproperty of the hearing sense with respect to an input audio signalwhich is a time signal, and a recording medium adapted so thatinformation in which characteristic of time signal information istransformed by such method or apparatus is recorded thereonto orthereinto.

BACKGROUND ART

Hitherto, as a technique for altering (changing) sound quality ofacoustic (audible) signal information, there are used, e.g., a system ofaltering the frequency characteristic by filtering processing, a systemfor producing higher harmonic (wave), a system of altering (changing)dynamic range by so called compressor, and the like.

However, in the case of the system using filter, how to use filter ischanged e.g., a medium frequency band is enhanced to improve presence,etc., thus to change sound quality. In the system of producing higherharmonic (wave), use in a manner of sound effect is applied rather thansound easy to be heard is obtained. In addition, the system of changing(altering) dynamic range by compressor is a system such that big soundis not caused to be disagreeable to the ear, or soft sound is not causedto be masked by the ambient noise. With these systems, it is difficultto carry out optimum control such that sound agreeable to the ear isprovided from a viewpoint of the hearing sense in a manner to cope withchanges of acoustic signal information varying moment by moment.

In view of actual circumstances as described above, this invention hasbeen proposed, and its object is to provide a signal transforming methodand a signal transforming apparatus capable of transforming speech andacoustic signals significant with respect to sound quality from aviewpoint of the hearing sense of the human being, and a recordingmedium adapted so that speech or acoustic signal information of whichcharacteristic is transformed by the above-mentioned method or apparatusis recorded thereonto or thereinto.

Namely, the task that this invention contemplates solving is to providean technique for implementing a predetermined transform processing toacoustic signal information to create sound which can be heard agreeablywith high quality from a viewpoint of sound quality for the human beingmoment by moment by using the auditive (auditory) principle (principlefrom a viewpoint of the hearing sense). Moreover, another task of thisinvention is to lessen, from acoustic signal information which has beenalready digitized so that quantizing (quantization) noises are addedthereto, auditive influence of such quantizing noises to thereby improvequality. A further task of this invention is to lessen, from audiosignal information which has been already digitized so that quantizingnoise are added thereto, auditive influence of quantizing noisesthereafter to create (prepare) data of which sound quality is improvedby auditive processing when recorded on compact disc having word lengthof 16 bits by the technology for reducing noise level from a viewpointof the hearing sense by altering (changing) spectrum of quantizing noiseso as to become in conformity with so called equi-loudnesscharacteristic or masking characteristic which has been already proposedas the technology for improving sound quality of audio equipment such asso called compact disc by the applicant of this invention (thistechnology will be referred to as, e.g., Super Bit Mapping technologyhereinafter), i.e., the technologies disclosed in, e.g., Tokkaihei No.2-20812 (Japanese Patent Application Laid Open No. 20812/1990),Tokkaihei No. 2-185552 (Japanese Patent Application Laid Open No.185552/1990), and Tokkaihei No. 2-185556 (Japanese Patent ApplicationLaid Open NO. 185556/1990). In accordance with the Super Bit Mappingtechnology, in the case of re-quantizing digital signal having wordlength beyond 16 bits for use in compact disc having 16 bit length,sound quality can be improved. A still further task of this invention isthat with respect to audio signal information to which quantizing noiseshave been already added, in equivalently improving, from a viewpoint ofhearing sense, sound quality so that its word length once becomes equalto 16 bits or more to re-quitize such audio signal information so thatits word length becomes equal to 16 bits for a second time, word lengthis caused to be 16 bits while maintaining S/N of the frequency bandimportant from a viewpoint of hearing sense in the state of 16 bits ormore, thereby improving sound quality.

DISCLOSURE OF THE INVENTION

A signal transforming method and a signal transforming apparatus arecharacterized in that with respect to frequency components obtained fromtime signal information, difference in magnitude of attribute is altered(changed) between corresponding frequency component (any one of thefrequency components) and at least one proximity frequency component.Here, acoustic time signal information is used as the time signalinformation wherein, with respect to frequency components obtained fromthe acoustic time signal information, difference in magnitude ofattribute is altered (changed) between corresponding frequency componentand any other frequency component or components within substantiallycritical band based on the hearing sense characteristic. Theabove-mentioned attribute is magnitude of frequency component.

Moreover, signal transforming method and signal transforming apparatusof this invention are characterized in that, with respect to frequencycomponents obtained from acoustic time signal information, difference inmagnitude of attribute is altered between corresponding frequencycomponent and any frequency component or components above the minimumaudible limit level or the masking threshold level of other frequencycomponents within substantially critical band, difference in magnitudeof attribute is altered between corresponding frequency component andany frequency component or components above level of a larger one of theminimum audible limit level and the masking threshold level of otherfrequency components within substantially critical band, or differencein magnitude of attribute is altered between corresponding frequencycomponent and any frequency component or components within a limitedlevel range of other frequency components within substantially criticalband, thereby to transform the characteristic of the acoustic timesignal information.

In addition, signal transforming method and signal transformingapparatus are characterized in that with respect to frequency componentobtained from acoustic time signal information having frequencyresolution and time resolution where at least two frequency componentsare different, difference in magnitude of attribute is altered betweencorresponding frequency component and any other frequency component orcomponents within substantially critical band to thereby transform thecharacteristic of the acoustic time signal information.

Here, in transforming the acoustic time signal information intofrequency components, an approach is employed to divide the acoustictime signal information into signals (signal components) in a pluralityof bands thereafter to orthogonally transform signals in respectivebands thus to obtain a plurality of frequency components. It should benoted that according as frequency shifts to lower frequency band side,frequency resolutions of the plural frequency components become higher.

Moreover, in altering (changing) the characteristic of the acoustic timesignal information, an approach described below is employed. Forexample, with respect to at least one local peak of a plurality offrequency components obtained from acoustic time signal information,difference in magnitude of attribute is altered (changed) betweencorresponding frequency component and any other frequency component orcomponents within substantially critical band. Further, difference inmagnitude of attribute is caused to be large between correspondingfrequency component and any other frequency component or components inthe frequency region having a frequency difference which is 10% to 50%of substantially critical bandwidth. In addition, frequency region wheredifference in magnitude of attribute of frequency component is alteredis determined by difference between two shift peak values of magnitudeof attribute of frequency component having different number of frequencycomponent samples. Frequency component in the frequency region wherevalue obtained by subtracting shift peak value of 10% width ofsubstantially critical bandwidth from shift peak value of 50% width ofsubstantially critical band width is negative is caused to be smaller orto be null (deleted). Magnitude of frequency component is adjusted so asto retain short time energy of time signal information. Magnitude offrequency component of at least one local peak is adjusted so as toretain short time energy of time signal information. Difference inmagnitude of attribute is altered (changed) between correspondingfrequency component and any frequency component or components withinlevel range limited by quantizing noise level.

Further, in accordance with the signal transforming method and thesignal transforming apparatus of this invention, re-quantizationprocessing having noise shape characteristic is implemented to timesignal information re-synthesized on the time base. At this time, noiseshape characteristic is dependent upon at least one of minimum audiblelimit, equi-loudness and masking characteristic.

In other words, the signal transforming method and apparatus of thisinvention implement filtering processing or orthogonal transformprocessing to input acoustic time signal to thereby obtain frequencycomponents. Then, shift peak values every adjacent components of thesefrequency components are obtained at two different frequency widthsrelating to the critical band to allow the magnitude of frequencycomponent in the frequency band where any difference between two kindsof shift peak values takes place to be smaller to thereby reduce thedegree of dissonance between local peak frequency component and anyother frequency component. In expanding input acoustic time signal onthe frequency base, components on the time base in a plurality offrequency bands are obtained by filter, etc. thereafter to use blockingfrequency analysis technique by orthogonal transform, etc., or tocascade-connect band division filters such as so called QMF (QuadratureMirror Filter), CQF (Conjugate Quadrature Filter), etc. in a manner oftree structure to thereby carry out band division such that, in a rangefrom lower frequency band to higher frequency band, frequency resolutiongradually becomes lower, and time resolution is oppositely improved.

At this time, there may be employed a method of carrying out blocking byblocks such that time length in lower frequency band is greater thanthat in higher frequency band to carry out orthogonal transformprocessing or take peak values of a plurality of samples on the timebase. Frequency bandwidth and time width of block are caused to havefrequency resolution which sufficiently satisfies critical bandwidth soas to become optimum from a viewpoint of hearing sense. Whether or notspectrum obtained by analysis is more than masking threshold level(threshold level of masking) is judged by its magnitude and frequency.In the case where that spectrum is less than the masking thresholdlevel, measure is taken such that attribute such as intensity or phase,etc. is not altered (changed). This similarly applies to the minimumaudible limit. With respect to frequency components below the minimumaudible limit, even if difference between shift peak values is not zero,measure is taken such that alteration is not made. Further, employmentof a method of allowing acoustic signal information processed in amanner described above to undergo super bit mapping processing tothereby reduce bit length is effective for most effectively preventingdegradation of sound quality when viewed from the hearing sense in thecase where recording/reproduction/transmission, etc. are carried out bylimited word length.

Further, in the case where level of quantizing noise which has beenalready added can be identified or expected, method of carrying outprocessing different from that of other components with respect tofrequency component of this level is effective for effectively removingadded quantizing noise. For example, employment of a method of givingattenuation greater than that of other components, or completelyremoving quantizing noise is effective. In addition, employment ofmethod of allowing acoustic signal information processed in a mannerdescribed above to undergo the super bit mapping processing to therebyreduce bit length is effective for most effectively preventingdegradation of sound quality from a viewpoint of hearing sense in thecase of carrying out recording/reproduction/transmission, etc. bylimited word length.

Moreover, recording medium of this invention is adapted so thattransformed data obtained after undergone processing by theabove-mentioned signal transforming method or apparatus is recordedthereon or therein. As such recording medium, magneto-optical disc,optical disc, semiconductor memory, IC memory card, and the like can beenumerated.

Accordingly, in accordance with the signal transforming method andsignal transforming apparatus of this invention, harmonious relationshipbetween frequency components within critical band supported from aviewpoint of hearing sense is controlled, thereby making it possible toadjust sound quality of speech and acoustic signals so that it isadvantageous to the human being. Moreover, employment of method ofmaking no alteration with respect to frequency components less thanmasking threshold and minimum audible limit is effective in allowingunnecessary processing irrelevant from a viewpoint of sound quality tobe carried out to the minimum degree, and preventing extra side effectssuch as connection distortion, etc. Further, employment of method inwhich although digital sample data recorded on compact disc has onlyresolution of word length of 16 bits, auditive alteration of frequencycomponent and super bit mapping processing are combined to prepare 16bit acoustic signal information to record it onto compact disc, etc. iseffective in the case of recording acoustic signal information to whichquantizing noise has been already added and acoustic signal informationincluding frequency components undesired from a viewpoint of hearingsense onto compact disc, digital audio tape, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing, in a block form, an example ofoutline of the configuration of a signal transforming apparatus of thisembodiment for realizing a method of transforming characteristic of timesignal information (signal transforming method) of this invention.

FIG. 2 is a view showing time blocks every respective frequency bandsaccording to this invention.

FIG. 3 is a view showing frequency shift peak according to thisinvention.

FIG. 4 is a view showing an example of frequency characteristic offrequency shift peak according to this invention.

FIG. 5 is a view showing the relationship between the degree ofconsonance and critical band.

FIG. 6 is a circuit diagram showing, in a block form, an example of theconfiguration of dissonant band detecting circuit of the embodimentaccording to this invention.

FIG. 7 is a circuit diagram showing, in a block form, an example of theconfiguration of masking threshold curve detecting circuit of theapparatus of the embodiment.

FIG. 8 is a view showing sum total value of signal components ofrespective critical bands.

FIG. 9 is a view showing sum total value of signal components ofrespective critical bands and masking threshold.

FIG. 10 is a view showing sum total value of signal components ofrespective critical bands, masking threshold, and minimum audible limit.

FIG. 11 is a view showing the example where the magnitude of frequencycomponent is altered.

FIG. 12 is a view showing an example of the configuration of feedbackfilter for noise shaping.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of this invention will now be described with reference tothe attached drawings.

A signal processing system of this embodiment to which a signaltransforming method of this invention is applied comprises, as shown inFIG. 1, band division filters 2, 3, 4 and MDCT circuits 5a, 5b, 5c, 5dwhich will be described later as transforming means for transformingacoustic time signal information into signals (signal components) in aplurality of frequency components; and a frequency component altering(changing) circuit 6, a mask circuit 10, a frequency (region) shift peakdetecting circuit 12, a dissonant frequency (region) detecting circuit11, a masking threshold curve detecting circuit 16, and a minimumaudible curve limit generating circuit 17 which will be described lateras attribute altering (changing) means such that, with respect to atleast one local peak of a plurality of frequency components obtained bythe above-mentioned transforming means, it alters (changes) differencein magnitude of attribute between corresponding frequency component andany other frequency component or components within substantiallycritical band based on the hearing sense characteristic.

Moreover, attribute altering (changing) means of signal transformingapparatus of this embodiment to which signal transforming method of thisinvention is applied is operative so that, with respect to a pluralityof frequency components obtained from the transforming means, it altersdifference in magnitude of attribute between corresponding frequencycomponent and any frequency component or components above minimumaudible limit level or masking threshold level of other frequencycomponents within substantially critical band, or that, with respect tofrequency components obtained from acoustic time signal informationhaving frequency resolution and time resolution where at least twofrequency components are different of a plurality of frequencycomponents obtained from the transforming means, it alters difference inmagnitude of attribute between corresponding frequency component and anyother frequency component or components within substantially criticalband.

Initially, FIG. 1 is circuit diagram showing, in a block form, anexample of outline of the configuration of signal processing systemconstituting a signal transforming apparatus of this embodiment whichrealize signal transforming method according to this invention aspreviously described above. Actual configuration of FIG. 1 will now bedescribed.

Namely, the signal transforming apparatus of this embodiment divides aninput digital signal such as speech (audio) or acoustic signalinformation (acoustic time signal information), etc. into signals(signal components) in a plurality of frequency bands, and makes aselection such that bandwidths of adjacent two bands of the lowestfrequency band are the same and that, in higher frequency bands,bandwidth becomes broader according as frequency shifts to higherfrequency band side therewithin to carry out orthogonal transformprocessing every respective frequency bands to determine, from spectrumdata on the frequency base obtained, information of shift peak curve infrequency region and masking curve in frequency region.

From information of the shift peak curve in frequency region, frequencycomponent is altered (changed) from harmonious relationship frequencycomponents to thereby obtain frequency band which can expect preferablechange of sound quality. Moreover, from information of masking curve infrequency region, frequency component which has been obtained frominformation of shift peak curve in the frequency region is altered tothereby determine frequency region or regions in which change of soundquality cannot be substantially expected by masking of frequency bandsin which preferable change of sound quality can be expected, thus toexclude such region(s) from frequency band caused to be subject toalteration (change) of frequency component. Also with respect tofrequency components below the minimum audible limit, they are excludedfrom frequency components subject to alteration. The magnitude of eachfrequency component within frequency band where the frequency componentis altered (changed) determined in this way is caused to be smaller orto be null (removed).

Then, frequency components are caused to undergo inverse orthogonaltransform processing to obtain time signal information to combine allbands by using synthesis filter to thereby obtained entire band timesignal information. Further, in quantization, super bit mappingprocessing to optimize, from a viewpoint of hearing sense, quantizingnoise spectrum within frequency band less than 20 Khz is carried out.

Explanation will be given in more detail with reference to FIG. 1. Inputterminal 1 is supplied with audio PCM signal of 0˜22 Khz when samplingfrequency is, e.g., 44.1 Khz. This input signal is divided into signalin 0˜11 Khz band and signal in 11 k˜22 Khz band by using band divisionfilter 2 such as CQF mentioned above, etc. The signal in the 0˜11 Khzband is similarly divided into signal in 0˜5.5 Khz band and signal in5.5 k˜11 Khz band by using band division filter 3 such as CQF filter,etc. Further, the signal in 0˜5.5 Khz band is similarly divided intosignal in 0˜2.75 Khz band and signal in 2.75˜5.5 Khz band by using banddivision filter 4.

The signal in 11 k˜22 Khz from band division filter 2 is sent to MDCT(Modified Discrete Cosine Transform) circuit 5a which is one example oforthogonal transform circuit, the signal in 5.5 k˜11 Khz band from banddivision filter 3 is sent to MDCT circuit 5b, the signal in 2.75 Khz˜5.5Khz band from band division filter 4 is sent to MDCT circuit 5c, and thesignal in 0 Khz˜2.75 Khz band from band division filter 4 is sent MDCTcircuit 5d. Thus, these signals are respectively caused to undergo MDCTprocessing. As a matter of course, orthogonal transform such as FastFourier Transform CFFT) or Discrete Cosine Transform (DCT), etc. may beapplied to these orthogonal transform circuits in addition to theabove-mentioned MDCT.

Here, as a technique for dividing an input digital signal into signals(signal components) in a plurality of frequency bands by band divisionfilter as described above, there is, e.g., technique using filter suchas the CQF, etc. This is described in Mark J. T. Smith and Thomas P.Barnwell, "Exact Reconstruction Techniques for Tree-Structured SubbandCoders," IEEE Trans. ASSP, Vol. ASSP-34 No. 3, June 1986, pp. 434-441.Moreover, in 1976 R. E. Crochiere Digital coding of speech in subbandsBell Syst. Tech. J. Vol. 55, No. 8 1976, technique using filter such asQMF, etc. is described. Further, in ICASSP 83, BOSTON PolyphaseQuadrature Filters-A new subband coding technique Joseph H. Rothweiler,technique for filter division of equal bandwidth is described.

In addition, as the above-described orthogonal transform, there is,e.g., such an orthogonal transform to divide input audio signal intoblocks every predetermined unit time (frame) to carry out, everyrespective blocks, e.g., Fast Fourier Transform (FFT), Discrete CosineTransform (DCT), or Modified DCT, etc. to transform signals on the timebase into signals on the frequency base. The above-mentioned MDCT isdescribed in ICASSP 1987 Subband/Transform Coding Using Filter BankDesigns Based on Time Domain Aliasing Cancellation J. P. Princen A. B.Bradley Univ. of Surrey Royal Melbourne Inst. of Tech.

Here, an actual example of a standard input signal with respect toblocks every respective frequency bands supplied to the above-mentionedrespective MDCT circuits 5a, 5b, 5c, 5d is shown in FIG. 2.

In the actual example of FIG. 2, the above-described four filter outputsignals have orthogonal transform block sizes different every respectivebands, and such a frequency analysis to sufficiently satisfy criticalbandwidth at respective frequencies is carried out. Thus, according asfrequency becomes higher, frequency resolution is lowered, but timeresolution is instead improved. In this embodiment, frequency resolutionis selected to such a degree that critical bands are substantiallydivided into ten bands, respectively. By this selection, it is possibleto carry out control of the magnitudes of frequency components withincritical band with frequency within critical band being considerablyfreely limited.

Namely, in this embodiment, in the frequency band from 0 Hz up to 2.75Khz, time block size of orthogonal transform processing is set to 46.4msec so that frequency resolution of approximately 10Hz which is onetenth of 100 Hz of the narrowest critical bandwidth of this band can beprovided. Similarly, in the 2.75 Khz to 5.5 Khz band, time block size oforthogonal transform processing of 11.6 msec is used so that frequencyresolution of 40 Hz is provided. In the 5.5 Khz to 11 Khz band, timeblock size of orthogonal transform processing of 5.8 msec is used sothat frequency resolution of 80 Hz is provided. In the 11 Khz to 22 Khzband, time block size of orthogonal transform processing of 2.9 msec isused so that frequency resolution of 160 Hz is provided. It should benoted that, because critical bandwidth at 11 Khz is approximately 3 kHz,employment of method in which orthogonal transform block size is furthercaused to be one half so that frequency resolution of 320 Hz is providedis effective in further improvement in time resolution. In Table 1,center frequencies and band widths of critical bands are shown.

                  TABLE 1A                                                        ______________________________________                                        Band No.     Center Frequency                                                                           Bandwidth                                            Bark!        Hz!          Hz!                                                ______________________________________                                        1             50           80                                                 2            150          100                                                 3            250          100                                                 4            350          100                                                 5            450          110                                                 6            570          120                                                 7            700          140                                                 8            840          150                                                 9            1000         160                                                 10           1170         190                                                 11           1370         210                                                 12           1600         240                                                 13           1850         280                                                 ______________________________________                                    

                  TABLE 1B                                                        ______________________________________                                        Band No.     Center Frequency                                                                           Bandwidth                                            Bark!        Hz!          Hz!                                                ______________________________________                                        14           2150         320                                                 15           2500         380                                                 16           2900         450                                                 17           3400         550                                                 18           4000         700                                                 19           4800         900                                                 20           5800         1100                                                21           7000         1300                                                22           8500         1800                                                23           10500        2500                                                24           13500        3500                                                25                                                                            ______________________________________                                    

Turning back to FIG. 1, frequency components or MDCT coefficient dataobtained after undergone MDCT processing at respective MDCT circuits 5a,5b, 5c, 5d are delivered to frequency shift peak detecting circuit 12and dissonant frequency detecting circuit 11 which serve to establishfrequency region where frequency component having dissonant relationshipwith respect to local peak frequency components, and masking thresholdcurve detecting circuit 16 for determining masking threshold curve.

The operation of the frequency shift peak detecting circuit 12 will nowbe described.

In FIG. 3, for easiness of understanding, method of taking shift peakvalues relating to three adjacent frequency components is explained.

Initially, with respect to shift peak value having component s1 ascenter, shift peak value is defined by magnitude of component havingmaximum magnitude of respective components s0, s1, s2 including thecomponent s1 and both components adjacent thereto. With respect to shiftpeak value having component s1 as center, shift peak value is defined bymagnitude of component having maximum magnitude of respective componentss1, s2, s3 including the component s2 and both components adjacentthereto. By determining peak values in succession in this way, shiftpeak value curve is obtained.

Illustration is made for easiness of understanding in FIG. 3 such thatfrequency components all have the same bandwidth and frequency widths atthe time of determining shift peak are equal. However, in thisembodiment, as shown in FIG. 4, according as frequency shifts to higherfrequency band side, frequency bandwidth that frequency component hasbecomes broader and shift peak value at frequency bandwidth which is 10%or 50% of critical bandwidth at that frequency is determined. In FIG. 4,BE1˜BE4 respectively represent frequency bands, curve P₁₀ representsshift peak curve of 10% of critical bandwidth, curve P₅₀ representsshift peak curve of 50% width of critical bandwidth, curve SD representsfrequency component distribution, and CB represents critical bandwidthsat respective frequencies. In this case, in frequency band where peakvalues are defined in overlapping manner, a larger one of peak values isselected.

It should be noted that the above-mentioned critical bandwidth isphysical quantity which can be satisfactorily understand the hearingsense characteristic of the human being such as consonance, sense ofmagnitude of noise, masking characteristic or the like, and consonancewill now be described with respect to this invention with reference toFIG. 5. FIG. 5 represents that when frequency difference between twofrequency components exists by frequency indicated on the abscissa (axisindicating frequency normalized by critical bandwidth), the degree ofconsonance or dissonance of these two frequency components is indicatedon the ordinate. In accordance with this result, in a range wherefrequency difference between two frequency components is 10% to 50% ofcritical bandwidth (dissonant sound band NHB), sense of dissonance takesplace (dissonant sound level NHL). In ranges of frequency differencefrom 0% to 10% and from 50% to 100% (consonant sound band HB), sense ofconsonance takes place (consonant sound level HL). It should be notedthat this critical bandwidth is such that according as frequency shiftsto higher frequency band side, bandwidth becomes broader.

Actual means for detecting dissonant band will now be described withreference to FIG. 6.

Frequency components or MDCT coefficient data obtained after undergoneMDCT processing at respective MDCT circuits 5a, 5b, 5c, 5d in FIG. 1 arecaused to undergo processing for obtaining absolute values, and are thendelivered to input terminal 41 of dissonant frequency detecting circuit11 as dissonant band detecting means shown in FIG. 8. In this case, lowfrequency band side characteristic having longer time width is usedcommonly to respective higher frequency band times.

From frequency components delivered to input terminal 41, two shift peakcharacteristics having different frequency widths can be obtained.Namely, by shift peak detecting circuit 42 of 10% width of criticalbandwidth which provides shift peak value of 10% width of criticalbandwidth and shift peak detecting circuit 43 of 50% width of criticalbandwidth which provides shift peak value of 50% width of criticalbandwidth, two shift peak characteristics having different frequencywidths can be obtained.

These shift peak curves obtained at shift peak detecting circuit 42 of10% width of critical bandwidth which provides shift peak value of 10%width of critical bandwidth and shift peak detecting circuit 43 of 50%width of critical bandwidth which provides shift peak value of 50% widthof critical bandwidth are caused to undergo processing for calculatingdifference therebetween by difference detecting circuit 44. Thedifference thus obtained is taken out from output terminal 45.

Frequency region where difference between shift peak values obtained inthis way is above certain threshold level is defined as dissonantfrequency region.

However, when other hearing sense effects, i.e., masking effect,equi-loudness, minimum audible limit are taken into consideration, thereis no necessity of allowing all frequency components included in thedissonant frequency region determined in a manner described above to besubject to operation. Namely, when masking effect, equi-loudness,minimum audible limit are taken into consideration, even if frequencycomponents judged not to be heard from a viewpoint of hearing sense areexcluded from frequency component subject to operation, there is hardlyinfluence. In addition, when equi-loudness is taken into consideration,method of allowing only frequency bands which are effective to besubject to operation is useful for reduction of operation quantity.

Mask circuit 10 having mask function, masking threshold curve detectingcircuit 16 having masking curve calculating function and minimum audiblecurve generating circuit 17 for storing minimum audible limitinformation in FIG. 1 are used in order to exclude, from frequencycomponent subject to operation, frequency components judged not to beheard from a viewpoint of hearing sense when masking effect and minimumaudible limit are taken into consideration as explained above.

Mask function at the mask circuit 10, masking curve calculating functionat masking threshold curve detecting circuit 16, and minimum audiblelimit memory function at minimum audible curve generating circuit 17will now be described in more detail.

FIG. 7 is a circuit diagram showing, in a block form, outline of theconfiguration of an actual example of masking curve calculating functionat the masking threshold curve detecting circuit 16.

In FIG. 7, input terminal 71 is supplied with frequency component datafrom respective MDCT circuits 5a, 5b, 5c, 5d in FIG. 1.

Input data on the frequency base is sent to circuit 72 for calculatingenergy every critical band, at which energies of respective criticalbands are determined by calculating sum total of respective amplitudevalues of frequency components within respective critical bands. Thereare instances where peak value or mean value of amplitude value, etc.are used in place of energies every respective critical bands. As outputfrom this energy calculating circuit 72, e.g., spectrum values of sumtotal value of respective bands are indicated as SB in FIG. 8. It shouldbe noted that the number of division bands is represented by 12 bands(B1˜B12) for brevity of illustration in FIG. 8.

In order to take into consideration influence in so called masking ofthe spectrum SB, such a convolution processing to multiply the spectrumvalues SB by a predetermined function to add them is implemented. Torealize this, output of energy calculating circuit 72 every band, i.e.,respective values of the spectrum SB are sent to convolution filtercircuit 73. The convolution filter circuit 73 is composed of, e.g., aplurality of delay elements for sequentially delaying input data, aplurality of multipliers (e.g., 25 multipliers corresponding torespective bands) for multiplying outputs from these delay elements byfilter coefficients (weighting function), and sum total adder for takingsum total of respective multiplier outputs. By this convolutionprocessing, sum total of the portion indicated by dotted lines in FIG. 8is taken with respect to, e.g., spectrum SB of band indicated by B6 inFIG. 8. It should be noted that the above-mentioned masking is thephenomenon that a signal is masked by another signal so that sound isnot heard. For such masking effect, there are successive masking effectby audio signal on the time base and simultaneous masking effect bysignal on the frequency base. By these masking effect, even if signalinformation or noises exist at the portion subject to masking, theywould not be heard. For this reason, in the case of actual audio signal,there is no necessity of allowing signal information and noise withinthe range subject to masking to be frequency component subject tooperation.

An actual example of multiplication coefficients (filter coefficients)of respective multipliers of the convolution filter circuit 73 will nowbe described. When coefficient of multiplier M corresponding to anarbitrary band is assumed to be 1, outputs of delay elements arerespectively multiplied by coefficient 0.15 at multiplier M-1,coefficient 0.0019 at multiplier M-2, coefficient 0.0000086 atmultiplier M-3, coefficient 0.4 at multiplier M+1, coefficient 0.06 atmultiplier M+2, and coefficient 0.007 at multiplier M+3. Thus,convolution processing of the spectrum SB is carried out. In this case,M is arbitrary integers of 1˜25.

Then, output of the convolution filter circuit 73 is sent to subtractor74. This subtractor 74 serves to determine (calculate) level αcorresponding to signal information or noise level which can be excludedfrom frequency component subject to operation that will be describedlater in the convoluted region. It is here noted that the level αcorresponding to signal information or noise level which can be excludedfrom the frequency component subject to operation is such a level tobecome equal to signal information or noise level which can be excludedfrom frequency components subject to operation every respective bands ofcritical band (critical bandwidth) by carrying out inverse convolutionprocessing. The subtractor 74 is supplied with allowed function(function representing masking level) for determining the level α. Byincreasing or decreasing this allowed function, control of the level αis carried out. This allowed function is delivered from (n-ai) functiongenerating circuit 75 as described below.

Namely, when numbers given in order from low frequency band of bands ofthe critical band are assumed to be i, level α corresponding to signalinformation or noise level which can be excluded from frequencycomponents subject to operation can be determined (calculated) by thefollowing formula (1).

    α=S-(n-ai)                                           (1)

In the formula (1), n and a(>0) are constant, S is intensity of barkspectrum, and (n-ai) in the formula (1) is allowed function. In thisembodiment, setting is made such that n=38 and a=1.

In this way, the above-mentioned α is determined. This data is sent todivider 76. This divider 76 serves to implement inverse convolution tothe level α in the convoluted region. Accordingly, by carrying out thisinverse convolution processing, masking spectrum can be obtained fromthe level α. Namely, this masking spectrum becomes signal information ornoise spectrum which can be excluded from frequency component subject tooperation.

It is to be noted while the inverse convolution processing requirescomplicated operation, simplified divider 76 is used in this embodimentto carry out inverse convolution.

The masking spectrum is sent to subtractor 78 through synthesis circuit77. This subtractor 78 is supplied with output of energy detectingcircuit 72 every critical band, i.e., the previously described spectrumSB through delay circuit 79. Accordingly, at this subtractor 78,subtractive operation between the masking spectrum and the spectrum SBis carried out. Thus, with respect to the spectrum SB, the portion belowlevel indicated by level of the masking spectrum MS is masked as shownin FIG. 9.

Output from the subtractor 78 is taken out through a circuit (of whichindication is omitted) for correcting signal information or noise levelwhich can be excluded from frequency component subject to operation andthrough output terminal 81. The output thus taken out is sent to themask circuit 10, at which frequency region which can be excluded fromvariable subject to operation of the dissonant frequency region isexcluded.

Delay circuit 79 is provided for delaying spectrum SB from energydetecting circuit 72 by taking into consideration delay quantities atrespective circuits preceding to the synthesis circuit 77. Meanwhile, insynthesis at the above-described synthesis circuit 77, it is possible tosynthesize data indicating so called minimum audible limit curve RCwhich is the hearing sense characteristic of the human being as shown inFIG. 10 delivered from minimum audible limit curve generating circuit 17and the masking spectrum MS. In this minimum audible limit curve, ifsignal or absolute noise level is less than this minimum audible limitcurve, signal and noise cannot be heard. This minimum audible limitcurve changes, e.g., in dependency upon difference of reproductionvolume at the time of reproduction. However, in realistic digitalsystem, it is considered that since there is not so difference in way ofentering of music into, e.g., 16 bit dynamic range, if quantizing noisein frequency band exceedingly easy to be heard to the ear cannot beheard, quantizing noise less than level of the minimum audible limitcurve cannot be heard in other frequency bands. Accordingly, when, e.g.,a way of use such that noise in the vicinity of 4 Khz of word lengththat system has is not heard is assumed to be adopted and the minimumaudible limit curve RC and the masking spectrum MS are synthesized sothat signal information or noise which can be excluded from frequencycomponent subject to operation is provided, signal information or noiselevel which can be excluded from frequency component subject tooperation can be as far as the portion indicated by slanting lines inFIG. 10.

In this embodiment, level of 4 Khz of the minimum audible limit curve isin correspondence with the minimum level corresponding to, e.g., 20bits. In FIG. 10, signal spectrum is indicated together.

As another method of limiting frequency component subject to operation,there are instances where such frequency component is limited by levelof quantizing noise included in input digital signal information. In thecase where spectrum is substantially white, since quantizing noise levelis substantially determined by word length, frequency component in thislevel range is caused to be limitedly frequency component subject tooperation, thereby making it possible to effectively reduce or eliminatecomponents which cause dissonance among quantizing noises. In FIG. 1,quantizing level storage function is caused to store quantizing noiselevel to thereby allow frequency component subject to operation tolimitedly fall within the range of this level. As a matter of course,quantizing level may be adjusted to optimum value.

Moreover, the circuit for correcting signal information or noise levelwhich can be excluded from frequency component subject to operationcorrects signal information or noise level which can be excluded fromfrequency component subject to operation in output from the subtractor78 on the basis of, e.g., information of equi-loudness curve sent fromcorrection information output circuit of which indication is omitted.Here, equi-loudness curve is characteristic curve relating to thehearing sense characteristic of the human being. This equi-loudnesscurve is obtained by determining sound pressures of sound at respectivefrequencies which can be heard at the same pitch as pure sound of, e.g.,1 Khz to connect them by curves, and is also called equi-sensitivitycurve of loudness. Moreover, this equi-loudness curve depictssubstantially the same curve as the minimum audible curve RC shown inFIG. 10. In this equi-loudness curve, e.g., in the vicinity of 4 Khz,even if sound pressure is lowered by 8˜10 Db as compared to that at 1Khz, sound can be heard at the same loudness (pitch) as that at 1 Khz.In contrast, in the vicinity of 10 Khz, if sound pressure is not higherthan sound pressure at 1 Khz by about 15 Db, such sound cannot be heardas sound of the same loudness (pitch). For this reason, it is seen thatmagnitude of signal or noise above level of the minimum audible curve isevaluated by frequency characteristic given by curve corresponding tothe equi-loudness curve. From facts described above, it is seen thatemployment of method of selecting signal information or noise which canbe excluded from frequency component subject to operation for thepurpose of reduction of quantity of operation by taking theequi-loudness curve into consideration is in conformity with the hearingsense characteristic of the human being.

Turning back to FIG. 1, the mask circuit 10 does not carry outalteration of frequency component in an unnecessary frequency band byusing the above-described hearing sense effect. This mask circuit 10outputs component information by which effective operation can beobtained in auditive improvement in sound quality of frequencycomponents having dissonant relationship with respect to local peakcomponent. Frequency component altering circuit 6 of FIG. 1 altersmagnitude of frequency component subject to operation on the basis ofthis information.

FIG. 11 shows the manner of altering magnitude of frequency component inthe frequency component altering circuit 6.

In FIG. 11, Band 1˜Band 4 are frequency regions where magnitude offrequency component designated by mask circuit 10 is altered. Degree ofalteration is such that according as corresponding position shifts tothe central portion of each band, it becomes greater. This utilizes thefact that degree of dissonance shown in the FIG. 5 mentioned abovechanges in dependency upon frequency difference. In the figure, SP1˜SP4represent gains at positions of respective local peak spectrumcomponents. They indicate that magnitude of spectrum at correspondingfrequency position is caused to be greater in order to compensationreduction of the entire energy resulting from the fact that frequencycomponent in dissonant frequency band becomes small.

Output of frequency component altering circuit 6 which has alteredmagnitudes of frequency components in this way is caused to undergoprocessing such that signals (signal components) on the frequency baseare transformed into signals (signal components) on the time base byIMDCT circuits 9a, 9b, 9c, 9d for carrying out inverse transformprocessing complementary to transform processing of the MDCT mentionedabove. IMDCT output signals from these IMDCT circuits 9a, 9b, 9c, 9d arefrequency-synthesized by band synthesis filters 13, 14, 15 havingfrequency synthesis (ICQF) function opposite to the above-mentioned CQFso that entire frequency band time signal is provided.

With respect to entire band signal by these band synthesis filters 13,14, 15, since there are instances dynamic range is caused to be greaterby change of frequency component as compared to the original inputsignal information, re-quantization into 16 bits may be required in thecase of recording it onto compact disc. It is to be noted that theapplicant of this invention has already disclosed such a technology toimplement, to input digital audio signal, re-quantization to providenoise frequency characteristic close to equi-loudness characteristic bynoise shaping in audio frequency band thus to record 16 bit re-quantizedsignal onto compact disc, e.g., in the previously described TokkaiheiNo. 2-20812 (Japanese Patent Application Laid Open No. 20812/1990)publication, Tokkaihei No. 2-185552 (Japanese Patent Application LaidOpen No. 185552/1990) publication, and Tokkaihei No. 2-185556 (JapanesePatent Application Laid Open No. 185556/1990). In accordance with thisinvention, in such a case, signal processed by this invention is furthercaused to undergo noise shaping, thereby making it possible to providecompact disc recording signal having characteristic above 16 bits.

The operation of noise shaper for carrying out the noise shaping willnow be described with reference to FIG. 1. Signal delivered from theband synthesis filter 15 delivered to adding circuit 18 is caused toundergo processing to take difference between that signal and outputsignal of feedback filter 21. Output of adding circuit 18 is deliveredto re-quantizer 19 and second adding circuit 20. The re-quantizer 19serves to carry out transmission/recording of signal by lesserinformation quantity as the result of the fact that output is providedby word length lesser than input signal word length. Output of thisre-quantizer 19 is delivered to output terminal 22 of this noise shapeand second adding circuit 20. This second adding circuit 20 serves toobtain difference between input and output of re-quantizer 19. Thus,quantization error is extracted as output. Output of second addingcircuit 20 is delivered to feedback filter 21.

The feedback filter will now be described in detail with reference toFIG. 12.

In FIG. 12, signal delivered to feedback filter 21 through terminal 50is sequentially shifted through a series circuit of delay elements 52,53, 54, 55. Outputs of the delay elements 52, 53, 54, 55 arerespectively to multiplying elements 56, 57, 58, 59. At thesemultiplying elements 56, 57, 58, 59, products of respective outputs ofdelay elements and filter coefficients delivered from correspondingcoefficient input terminals 62, 63, 64, 65 are provided. Outputs ofthese multiplying elements 56, 57, 58, 59 are added at adding element60. Added result is guided (delivered) to output terminal 61 of thefeedback filter.

Digital audio signal to which noise frequency characteristic close toequi-loudness characteristic is given by noise shaper constituted byadding circuit 18, re-quantizer 19, second adding circuit 20 andfeedback filter 21 mentioned above is outputted from output terminal 22.This output signal is caused to undergo predetermined error correctionprocessing, etc. The error corrected signal thus obtained is recordedonto or into recording medium (magneto-optical disc, optical disc,semiconductor memory, IC memory card).

It should be noted that transformed data formed by the embodiment ofthis invention may be transmitted through transmission path in additionto recording onto or into recording medium.

In addition, this invention is not limited to the above-describedembodiment, but may be applied to picture signal information, etc.

Industrial Applicability

In accordance with this invention, from facts as described above,predetermined transform processing is implemented to acoustic signalinformation, thus making it possible to create sound which is heardagreeable with high quality from a viewpoint of sound quality for thehuman being moment by moment by using the auditive principle. Moreover,approach is employed to lessen, from acoustic signal information whichhas been already digitized so that quantizing noises are added thereto,auditive influence of such quantizing noises, thus making it possible toimprove quality. Further, approach is employed to lessen, from audiosignal information which has been already digitized so that quantizingnoises are added thereto, auditive influence of quantizing noise,whereupon technology for reducing noise level from a viewpoint of thehearing sense by altering spectrum of quantizing noise so as to becomein conformity with so called equi-loudness characteristic or maskingcharacteristic is used as technology for improving sound quality ofaudio equipment like compact disc, thus making it possible create dataof which sound quality is improved by auditive processing at the time ofrecording onto compact disc having word length of 16 bits. Thus, in thecase of re-quantizing digital signal having word length above 16 bitsfor use in compact disc having 16 bit length, sound quality can beimproved. In addition, in accordance with this invention, inequivalently improving, from a viewpoint of hearing sense, sound qualityof audio signal information to which quantizing noises have been alreadyadded so that its word length becomes equal to 16 bits or more tore-quantize such audio signal information so that its word lengthbecomes equal to 16 bits for a second time, word length is caused to be16 bits while maintaining S/N of the frequency band important from aviewpoint of hearing sense in the state of 16 bits or more, therebymaking it possible to improve sound quality.

What is claimed is:
 1. A signal transforming method in which, withrespect to frequency components obtained from time signal information,difference in magnitude of attribute is altered between any one of thefrequency components and at least one proximate frequency component,wherein an amount of alteration is determined by a subset of a totalnumber of frequency components which exist in a critical band.
 2. Asignal transforming method as set forth in claim 1, wherein the timesignal information is acoustic time signal information.
 3. A signaltransforming method in which, with respect to frequency componentsobtained from acoustic time signal information, difference in magnitudeof attribute is altered between any one of the frequency components andany other frequency component or components within a substantiallycritical band based on the hearing sense characteristic, wherein anamount of alteration is such that after alteration the difference isapproximately equal to zero.
 4. A signal transforming method in which,with respect to at least one local peak of a plurality of frequencycomponents obtained from acoustic time signal information, difference inmagnitude of attribute is altered between the frequency component of thelocal peak and any other frequency component or components within asubstantially critical band based on the hearing sense characteristic,wherein an amount of alteration is such that after alteration thedifference is approximately equal to zero.
 5. A signal transformingmethod in which, with respect to frequency components obtained fromacoustic time signal information, difference in magnitude of attributeis altered between any one of the frequency components and any frequencycomponent or components above minimum audible limit level or maskingthreshold level of other frequency components within a substantiallycritical band to thereby transform the characteristic of the acoustictime signal information, wherein an amount of alteration is such thatafter alteration the difference is approximately equal to zero.
 6. Asignal transforming method in which, with respect to frequencycomponents obtained from acoustic time signal information, difference inmagnitude of attribute is altered between any one of the frequencycomponents and any frequency component or components above a larger oneof minimum audible limit level and masking threshold level of otherfrequency components within a substantially critical band, wherein anamount of alteration is such that after alteration the difference isapproximately equal to zero.
 7. A signal transforming method in which,with respect to frequency components obtained from acoustic time signalinformation, difference in magnitude of attribute is altered between anyone of the frequency components and any frequency component orcomponents within a limited level range of other frequency componentswithin a substantially critical band, thus to transform thecharacteristic of the acoustic time signal information, wherein anamount of alteration is such that after alteration the difference isapproximately equal to zero.
 8. A signal transforming method as setforth in claim 7, wherein difference in magnitude of attribute isaltered between any one of the frequency components and any frequencycomponent or components within a level range limited by quantizing noiselevel.
 9. A signal transforming method in which, with respect tofrequency components obtained from acoustic time signal informationhaving frequency resolution and time resolution where at least twofrequency components are different, difference in magnitude of attributeis altered between any one of the frequency components and any frequencycomponent or components within a limited level range of other frequencycomponents within a substantially critical band, wherein an amount ofalteration is such that after alteration the difference is approximatelyequal to zero.
 10. A signal transforming method as set forth in claim 9,wherein the acoustic time signal information is divided into signals ina plurality of frequency bands thereafter to orthogonally transform thesignals in respective frequency band, thus to obtain a plurality offrequency components.
 11. A signal transforming method as set forth inclaim 10, wherein frequency resolutions of the plurality of frequencycomponents become higher according as frequency shifts to lowerfrequency band side.
 12. A signal transforming method as set forth inany one of claims 9, to 11, wherein, with respect to frequencycomponents obtained from acoustic time signal information, difference inmagnitude is altered between any one of the frequency components and anyfrequency component or components above minimum audible limit level ormasking threshold level of other frequency components within asubstantially critical band.
 13. A signal transforming method as setforth in any one of claims 9 to 11, wherein, with respect to frequencycomponents obtained from acoustic time signal information, difference inmagnitude of attribute is altered between any one of the frequencycomponents and any frequency component or components above a larger oneof minimum audible limit level and masking threshold level of otherfrequency components within a substantially critical band.
 14. A signaltransforming method as set forth in any one of claims 9 to 11, wherein,with respect to frequency components obtained from acoustic time signalinformation, difference in magnitude of attribute is altered between anyone of the frequency components and any frequency component orcomponents within a limited level range of other frequency componentswithin a substantially critical band.
 15. A signal transforming methodas set forth in any one of claims 5 to 11, wherein, with respect to atleast one local peak of a plurality of frequency components obtainedfrom the acoustic time signal information, difference in magnitude ofattribute is altered between the frequency component of the local peakand any other frequency component or components within a substantiallycritical band.
 16. A signal transforming method as set forth in any oneof claims 3 to 11, wherein difference in magnitude of attribute isaltered between any one of the frequency components and any otherfrequency component or components in a frequency region having afrequency difference of 10% to 50% of the substantially criticalbandwidth.
 17. A signal transforming method as set forth in any one ofclaims 3 to 11, wherein a frequency region where difference in magnitudeof attribute of the frequency component is altered is determined bydifference between two shift peak values obtained from the frequencycomponents.
 18. A signal transforming method as set forth in any one ofclaim 1 to 11, wherein magnitude of frequency component is adjusted soas to retain short time energy of the time signal information.
 19. Asignal transforming method as set forth in claim 18, wherein magnitudeof frequency component of at least one local peak is adjusted so as toretain short time energy of the time signal information.
 20. A signaltransforming method as set forth in any one of claims 3 to 11, wherein afrequency component in a frequency region where a value obtained bysubtracting a shift peak value of 10% width of the substantiallycritical bandwidth from a shift peak value of 50% width of thesubstantially critical bandwidth is negative is caused to be small ornull (deleted).
 21. A signal transforming method as set forth in any oneof claims 5 to 11, wherein time signal information re-synthesized on thetime base is caused to undergo re-quantization processing having noiseshape characteristic.
 22. A signal transforming method as set forth inclaim 21, wherein the noise shape characteristic is dependent upon atleast one of minimum audible limit, equi-loudness and maskingcharacteristic.
 23. A signal transforming method as set forth in any oneof claims 1 to 11, wherein the attribute is magnitude of frequencycomponent.
 24. A signal transforming apparatus comprising:transformingmeans for transforming time signal information into frequencycomponents; and attribute altering means for altering difference inmagnitude of attribute between any one of the frequency components andat least one proximate frequency component, wherein an amount ofalteration is determined by a subset of a total number of frequencycomponents which exist in a critical band.
 25. A signal transformingapparatus as set forth in claim 24, wherein the time signal informationis acoustic time signal information.
 26. A signal transforming apparatuscomprising:transforming means for transforming acoustic time signalinformation into frequency components; and attribute altering means suchthat, with respect to the frequency component obtained from thetransforming means, it alters difference in magnitude of attributebetween any one of the frequency components and any other frequencycomponent or components within a substantially critical band based onthe hearing sense characteristic, wherein an amount of alteration issuch that after alteration the difference is approximately equal tozero.
 27. A signal transforming apparatus comprising:transforming meansfor transforming acoustic time signal information into a plurality offrequency components; and attribute altering means such that, withrespect to at least one local peak of the plurality of frequencycomponents obtained from the transforming means, it alters difference inmagnitude of attribute between the frequency component of the local peakand any other frequency component or components within a substantiallycritical band based on the hearing sense characteristic, wherein anamount of alteration is such that after alteration the difference isapproximately equal to zero.
 28. A signal transforming apparatuscomprising:transforming means for transforming acoustic time signalinformation into frequency components; and attribute altering means suchthat, with respect to the frequency component obtained from thetransforming means, it alters difference in magnitude of attributebetween any one of the frequency components and any frequency componentor components above minimum audible limit level or masking thresholdlevel of other frequency components within a substantially criticalband, wherein an amount of alteration is such that after alteration thedifference is approximately equal to zero, thus to transform thecharacteristic of the acoustic time signal information.
 29. A signaltransforming apparatus comprising:transforming means for transformingacoustic time signal information into frequency components; andattribute altering means such that, with respect to the frequencycomponents obtained from the transforming means, it alters difference inmagnitude of attribute between any one of the frequency components andany frequency component or components above a larger one of minimumaudible limit level and masking threshold level of other frequencycomponents within a substantially critical band, wherein an amount ofalteration is such that after alteration the difference is approximatelyequal to zero, thus to transform the characteristic of the acoustic timesignal information.
 30. A signal transforming apparatuscomprising:transforming means for transforming acoustic time signalinformation into frequency components; and attribute altering means suchthat, with respect to the frequency components obtained from thetransforming means, it alters difference in magnitude of attributebetween any one of thee frequency components and any frequency componentor components within a limited range of other frequency componentswithin a substantially critical band, wherein an amount of alteration issuch that after alteration the difference is approximately equal tozero, thus to transform the characteristic of the acoustic time signalinformation.
 31. A signal transforming means comprising:transformingmeans for transforming acoustic time signal information into frequencycomponents; and attribute altering means such that, with respect tofrequency components obtained from acoustic time signal having frequencyresolution and time resolution where at least two frequency componentsare different of the frequency components obtained from the transformingmeans, it alters difference in magnitude of attribute between any one ofthe frequency components and any other frequency component or componentswithin a substantially critical band, wherein an amount of alteration issuch that after alteration the difference is approximately equal tozero, thus to transform the characteristic of the acoustic time signalinformation.
 32. A signal transforming apparatus as set forth in claim31, wherein the transforming means divides the acoustic time signalinformation into signals in a plurality of frequency bands thereafter toorthogonally transform the signals in respective frequency bands, thusto obtain a plurality of frequency components.
 33. A signal transformingapparatus as set forth in claim 32, wherein the transforming means issuch that according as frequency shifts to lower frequency band side,frequency resolutions of the plurality of frequency components becomehigher.
 34. A signal transforming apparatus as set forth in any one ofclaims 31 to 33, wherein the attribute altering means is operative sothat, with respect to frequency components from acoustic time signalinformation, it alters difference in magnitude of attribute between anyone of the frequency components and any frequency component orcomponents above minimum audible limit level or masking threshold levelof other frequency components within a substantially critical band. 35.A signal transforming apparatus comprising:transforming means fortransforming acoustic time signal information into frequency components;and attribute altering means such that, with respect to the frequencycomponents from the acoustic time signal information by the transformingmeans, it alters difference in magnitude between any one of thefrequency components and any frequency component or components above alarger level of minimum audible limit level and masking threshold levelof other frequency components within a substantially critical band,wherein an amount of alteration is such that after alteration thedifference is approximately equal to zero, thus to transform thecharacteristic of the acoustic time signal information.
 36. A signaltransforming apparatus as set forth in any one of claims 31 to 33 or 35,wherein the attribute altering means is operative so that, with respectto frequency components obtained from acoustic time signal information,it alters difference in magnitude of attribute between any one of thefrequency components and any frequency component or components within alimited level range of other frequency components within a substantiallycritical band.
 37. A signal transforming apparatus as set forth in claim30 to 33 or 35, wherein the attribute altering means alters differencein magnitude of attribute between any one of the frequency componentsand any frequency component or components within a level range limitedby quantizing noise level.
 38. A signal transforming apparatus as setforth in any one of claims 28 to 33 or 35, wherein the attributealtering means is operative so that, with respect to at least one localpeak of a plurality of frequency components obtained from acoustic timesignal information, it alters difference in magnitude of attributebetween any one of the frequency components and any other frequencycomponent or components within a substantially critical band.
 39. Asignal transforming apparatus as set forth in any one of claims 26 to 33or 35, wherein the attribute altering means allows difference inmagnitude of attribute to be large between any one of the frequencycomponents and any other frequency component or components in afrequency region having a frequency difference of 10% to 50% of thesubstantially critical bandwidth.
 40. A signal transforming apparatus asset forth in any one of claims 26 to 33 or 35, wherein the attributealtering means determines a frequency region where difference inmagnitude of attribute of frequency component is altered by a differencebetween two shift peak values of magnitude of attribute of frequencycomponents having different frequency component sample numbers.
 41. Asignal transforming apparatus as set forth in any one of claims 24 to 33or 35, wherein the attribute altering means adjusts magnitude offrequency component so as to retain short time energy of time signalinformation.
 42. A signal transforming apparatus as set forth in claim41, wherein the attribute altering means adjusts magnitude of afrequency component of at least one local peak so as to retain shorttime energy of time signal information.
 43. A signal transformingapparatus as set forth in any one of claims 26 to 33 or 35, wherein, atthe attribute altering means, a frequency component of a frequencyregion where a value obtained by subtracting shift peak value of 10%width of the substantially critical bandwidth from a shift peak of 50%width of the substantially critical band is negative is caused to besmall or null (deleted).
 44. A signal transforming apparatus as setforth in any one of claims 28 to 33 or 35, which comprises re-quantizingprocessing means for implementing re-quantization having noise shapecharacteristic to time signal information re-synthesized on the timebase.
 45. A signal transforming apparatus as set forth in claim 44,wherein the noise shape characteristic at the re-quantizing processingmeans is dependent upon at least one of minimum audible limit,equi-loudness and masking characteristic.
 46. A signal transformingapparatus as set forth in any one of claims 24 to 33 or 35, wherein theattribute is magnitude of frequency component.
 47. A signal transformingmethod comprising the steps of:obtaining frequency components from asignal; reducing the difference in magnitude of attribute between alocal peak frequency component and a second frequency component; whereinthe local peak frequency component and the second frequency componentare within a substantially critical band, wherein the difference isreduced by increasing the magnitude of attribute of the second frequencycomponent, wherein the difference is made to be approximately equal tozero.
 48. A signal transforming method as set forth in claim 47, whereindifference local peak frequency component and the second frequencycomponent have a frequency difference of 10% to 50% of the substantiallycritical bandwidth.
 49. A signal transforming method as set forth inclaim 47, wherein the magnitude of attribute of the second frequencycomponent is adjusted so as to retain short time energy of the timesignal information.
 50. A signal transforming method as set forth inclaim 47, wherein a frequency component in a frequency region where avalue obtained by subtracting a shift peak value of 10% width of thesubstantially critical bandwidth from a shift peak value of 50% width ofthe substantially critical bandwidth is negative is caused to be smallor null (deleted).